The invention relates to a method of carrying out polymerization reactions in a reactor, with monomers and/or prepolymers being introduced (metered) into the reactor.
Polymerization comprehends the conversion of low molecular mass compounds (monomers, oligomers) into high molecular mass compounds (polymers, macromolecules). Industrially, polymers can be prepared under heterogeneous or homogeneous conditions. By heterogeneous reactions are meant polymerization in suspension/emulsion and precipitation reactions. These polymerization methods in suspension/emulsion are normally carried out in stirred tanks.
Precipitation polymerization takes place frequently using the thermodynamic separation of the polymer from its monomer and/or from a solvent. A prerequisite for this is that the polymer is insoluble in the monomer or solvent. In this type of preparation the polymer is precipitated.
Heterogeneous polymerization is normally realized on belt reactors [for PIB (polyisobutylene), PVBE (polyvinyl isobutyl ether)] or in kneading reactors [for SPS (syndiotactic polystyrene), POM (polyoxymethylene)]. In the belt reactor, owing to the large vapor passages, it is possible to control the polymerization temperature by evaporation of the solvent, but there is no movement of material and hence also no renewal of product surface. In the conventional kneading reactors (e.g., those from the companies Kurimoto and Mitsubishi Heavy Industries), on the other hand, an intensive renewal of product surface takes place, but there are no vapor passages present for evaporative cooling, so that the heat can be taken off only via contact with the cooled double jacket.
Polymerization reactions under homogeneous conditions have to date taken place only above the glass transition temperature or melting point of the polymer, i.e., they are realized in the melt. The company Sulzer Chemtec has developed, for example, a continuous, homogeneous polymerization of styrene and MMA (methyl methacrylate) in a circulation reactor with static mixing elements. This process requires high temperatures in order to keep the viscosity of the reaction mass low and so to avoid deposits on the reactor walls and on the mixing elements. Such high temperatures, however, have unwanted side effects, such as the formation of oligomers or depolymerization.
It is an the object of the present invention to provide a method of the type specified above in which the polymerization reaction under homogeneous conditions is substantially improved.